text:
How does the static pressure system keep the ambient pressure?
I understand that the compressed airflow around the aircraft effectively lowers the air pressure, and that's the reason why the alternate air switch affects your altimeter — it uses the slightly lower pressure in the cabin as reference — or why fuel is sucked out of the tanks if you forget your fuel caps.
This begs the question, what in the design of the static pressure system makes it more closely match the ambient pressure? Why is it unaffected by the effects affecting the cabin pressure?

Hi falstro! Do you mean "lowered per Bernoulli's principle or Venturi's effect"? If so: Why isn't "static" pressure speed-dependent?

BTW, I know @JayCarr suggested it, but "begs the question" means something completely different than what most English speakers use it for. Raises the question is more accurate.

@mins so in other words, someone is trying their darndest to place the static port somewhere where the effects are as small as possible, while never really succeeding. Would be cool to know how you usually go about looking for that spot though.

That's what I understand after the discussion conclusion. I'm curious too. BTW "it uses the slightly lower pressure in the cabin", is this what you wanted to write? (I feel you assume the lowest pressure is outside the cabin.)

There is a pretty good explanation in this answer. Hm, perhaps this could be marked duplicate; the question does appear to be a generalization of this one. Though; maybe not. It is answered there, but not in the accepted answer.

Possible duplicate of Which air stream pressure / speed is measured by the pitot?

@JanHudec that answer is a mile long, I didn't immediately spot what you're referring to and the question asks something completely different. Can we please ease up on the happy close-as-duplicate trigger fingers? :P If you want, collect the relevant parts of that answer, refer to it and post an answer :(

@JanHudec Not to mention that someone actually might want to explain it a bit more in-depth. Since this question actually asks about it, as opposed to the other question. There might be more answers. And so on.

Yes the other question is about pitot-static, and while static pressure is being mentioned it's not in the selected answer. Not a duplicate. This question deserves to have a complete answer here imho.

This question is really interesting as it brings to light a problem in the way Bernoulli's principle is presented to pilots in some ground courses and texts.
TL;DR: the low pressure is caused by curvature of the flow, not high speed itself, so we can place static ports on flat areas of fuselage that lie parallel to the air flow.
To re-state the question, OP (who is presumably learning to fly light aircraft) has been taught that the speed of the airflow around an aircraft is responsible for various low-pressure effects, e.g. fuel being sucked out of tanks and over-reading altimeter when using the alternate static source.

NOTE: For those unfamiliar, when OP refers to "alternate air switch" they are talking about a setup that is present in some light unpressurised training aircraft, e.g. the Piper PA-28-161 (as optional equipment) which have a valve under the instrument panel that can be used in the event of a blockage in the static pressure vents that feed the altimeter, ASI and VSI. This valve opens the static pressure system to cockpit air pressure. This can cause the errors in the altimeter reading, due to pressure in the cockpit being different to the free-stream static air pressure, but not as grave as the errors that would occur with a completely blocked static system.

Clarifying Bernoulli's Principle
Student pilots are usually taught that a wing flies because its shape causes airflow over the top to go faster than that below and, by the Bernoulli principle, this creates a region of lower pressure on the top surface, generating lift.
While this is true, it might lead one to think that this principle of "high speed = low pressure" applies all over the aircraft, so the OP is understandably puzzled about how it is possible to place a static pressure port anywhere on the aircraft such that it reads the correct value.
However, Bernoulli's principle only deals with changes to pressure due to changes in velocity (within a certain flow field) but doesn't say anything about the absolute value of the pressure. It can be thought of as a restatement of Newton's second law (F=ma) applied to fluids (and can be derived from it.) In other words, to change the velocity (speed or direction) of a flow, one must apply a force to it (in the form of a pressure difference.)
The airflow at a distance from an aircraft, while it may be at very high speed, is still only at ambient pressure (which depends only on the altitude we're flying at.)
As the airflow encounters the fuselage, the static pressure will change, but only if the velocity (speed or direction) of the flow changes.
For example, if you bring the air flow to a complete halt (e.g. at the tip of the pitot tube) its static pressure goes up to its peak value (called the total pressure.) Whereas when the airflow encounters a curved surface, the static pressure goes down. This is required in order to accelerate the flow around the surface and keep it attached. However, once the flow straightens out again, it returns to the free stream (ambient) value.
So along surfaces of the fuselage that lie parallel with the air flow, no acceleration (or deceleration) of the flow occurs and the pressure will be equal to that of the ambient air through which the aircraft is flying. If this this wasn't true, and we pretend for a minute that such a surface is at a pressure lower than ambient, this pressure difference would cause an in-flow of air toward the surface (perpendicular to the flight direction,) which would eventually equalise the pressure and bring it back to the ambient value again.
Placement of static ports
This means that parts of the fuselage that are parallel to the airflow and away from protuberances (like wings, struts, etc.) are good locations for the static ports and will read true ambient pressure during normal flight. Side-slipping (beta) can change this, which is why there is often a pair of static ports, one on either side of the fuselage.
Confirmation or fine-tuning of the static port placement can be done during the design of the aircraft by computational modelling of the flow (CFD) or by wind tunnel testing, then verified in the flight test programme (as described in one of the other answers.) If the placement is correct, there is little need for calibration of static port readings, or even the ability to do this on most light aircraft. There are, however, often published corrections for pitot (dynamic) pressure (CAS vs IAS.)
Another good location for a static port is in the form of one or more holes on the side of the pitot probe, as this is usually somewhere near the front of the aircraft in undisturbed air. This is where the static vent is placed on the PA-28-161.
Here's a lovely diagram from French Wikipedia (image credit), reproduced from "AGARD Flight Test Instrumentation Series, Volume 11", that shows the static pressure error along the fuselage of an aircraft. The red line shows the error due to the body only and the magenta line is that due to the combined body, wing and tail. The numbered blue lines show locations where the error is zero - these would be suitable places to put a static port.

Static pressure in the cockpit
The slightly reduced pressure in the cockpit of a PA-28 is due to the shape of the aircraft and where its openings (vents, etc.) are, not the speed of the air as such. For example, there are no pressure seals around the control cables which lead to the low-pressure area at the base of the rudder, but there are good seals on services that go through the firewall, meaning that you don't see much high pressure (ram air effect) from the nose area. Fun experiment: try opening the air vents with alternate static selected, to see if that makes a difference. Note that the flight manual says not to do this if actually making use of the alternate port in an emergency. Specifically, one edition of the PA-282-161 Warrior manual I looked at says "the storm window and cabin vents must be closed and the cabin heater and defroster must be on during alternate static operation." It states that under these conditions the error will be less than 50ft (unless otherwise placarded), which isn't bad at all.

It is feasible from an engineering point of view because one has ram pressure, which is higher than ambient, and also lower than ambient pressure caused by movement of air past the static port.
The latter is essentially the "aspirator effect", where the moving fluid (water or air) stream will pull air molecules out of the static port due to the viscous properties of air.
This is also "fuel sucked out of the fuel tanks if you forgot the gas caps"
So one finds places on the fuselage where these effects equally cancel each other out.
One might imagine how difficult this would be for a supersonic aircraft, but apparently subsonic aircraft are able to find the low tech, simple, and reliable solution as to where static ports should be placed.  These locations can be validated with in flight and wind tunnel testing.


text:
How am I supposed to track to KOSAX on the OLIVI 4W out of EDFM?
The SID chart for Mannheim, Germany (EDFM) runway 27 has segments to OLIVI are not defined in terms of any navigational aids but simply specify a track.
How am I supposed to fly these accurately? And more to the point, how am I supposed to determine that I'm over KOSAX? Dead reckoning? You might think that the SID requires GPS or other RNAV equipment, but there is another chart for that (which is virtually identical, but uses GPS-fix symbols instead of intersections).
KOSAX is also not shown on the Lower Enroute chart, which might otherwise have helped to determine its location.

I just know I'm missing the point.  What aircraft?  What fit?  I assume that the GPS/FMC don't understand waypoints?  Please add a bit more detail because as the question stands, it seems like 6DME MND then 333 for a bit of dead reckoning.  As far as determining the location of KOSAX, why is the lat long not enough?

@Simon lat/lon would require a GPS or INS or other RNAV equipment do determine accurately (and GPS has its own chart). Given that this is an instrument procedure, I would assume you'd have instrument support to fly it accurately. If you're saying dead-reckoning is the answer, then it's the first instrument procedure using dead-reckoning I've ever come across (not saying it's wrong, just that I didn't know it was acceptable)

Can't tell from the chart but isn't KOSAX->OLIVI on R294 from MND? What is the text description saying on OLIVI 4W?

@Radu094 MND is a DME, no radials available. The text just says to track 333° to KOSAX. But I found the answer in the remarks section of the textual description.

Ouch! I see MND now. Well, for that matter how can you fly to 6DME if you have no lateral guidance? Note that all IFR acft are required to have Basic-RNAV in EASA and DR segmments are allowed up to (i believe) 10 or 15 NM

@Radu094 yup, that's the answer. Did not know of the B-RNAV requirement. How to track 256° off the threshold to 6 DME is also a mystery, but I assume BRNAV again :p

@Radu094 it must be more than the 15 NM though, the segment KOSAX-OLIVI is 27 miles, all in all (and it does appear to be BRNAV all the way from takeoff to OLIVI) it's about 43 NM

If you are using BRNAV I think it's fair to say you are not dead-reckoning. There was a 10 or 15 mile limitation on DR for non (B)RNAV procedures, just using classic VOR/DMEs; I just can't find any reference about it anymore...

The textual description for OLIVI 4W is:
OLIVI FOUR WHISKEY
On track 256° to 6.0 DME MND; RT, on track 333° to KOSAX;
LT, on track 294° to OLIVI.
Climb with 7.9% (480 ft/NM) or more until passing 3000,
then climb with 6.4% (390 ft/NM) or more until passing 6000.

However, the remarks section holds the answer:
1. PDG 7.9% (480 ft/NM) due to obstacles.
   If unable to comply, request alternative instruction by ATC.
2. PDG 6.4% (390 ft/NM) due to airspace structure.
3. After 6.0 DME MND BRNAV equipment necessary.
4. During activity of ED-R 205 (TRA) MAX FL80.

Note "3. After 6.0 DME MND BRNAV equipment necessary."
BRNAV in this case means "Basic RNAV", which is essentially a form of RNAV equipment, but with less stringent certification requirements compared to normal IFR RNAV equipment.

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text:
What regulatory bodies are there?
Since planes traverse the Earth, and a country may deem another country's airline unsafe, yet that unsafe airline is deemed safe in its country, what is the hierarchy of the aviation regulatory bodies from the highest global level down to a state or even a town.
One example of how it moves top-down would be great.

6.0221413 * 10^23 regulations....or so it seems. This question is way too broad.

I think you mean how many regulating bodies, or sets of regulations, such as the FAA, EASA, ICAO, etc.

First, if you can come to a number, I do not see how it can be too broad. May it be 1, 10 or gooooogle regulations, it still ONE answer. And a pretty short one, too. That said, maybe someone can correct the question with the appropriate terms to specify "set of regulations", not the number of single subparagraphs.

@JonathanWalters: I was writing exactly that :-D Would you kindly edit the question with a better wording? :-)

fundamentally, each country has its own, EASA being the exception. what are the main ones? define "main ones".

Why was this closed as too broad? It is a classical question in basic aviation law, and perfectly answerable (as I think I have demonstrated)

@J.Hougaard: While I did vote to close it, it was for "not clear". VTR as your answer provides a clear direction. The question is not clear because there are different types of regulations: For aircraft, for pilots, for companies, for passengers, for airports, for search and rescue, for radio frequencies allocation, etc. Also "As planes fly all around the world they move from nation to nation" is not very relevant to all types. Last, in France I think all regulations are implemented in fine at the national level, even if France is part of EU, ICAO and WARC, etc.

Aviation regulations don't really stop at the national level, though. Just listing all of the individual states and municipalities in the U.S. alone that have aviation regulations would be way too broad to answer. I would be surprised if it's not the case that every U.S. state has aviation regulations and many municipalities (both in the U.S. and around the world) have them, too. Granted, these tend to be more related to things like noise abatement than safety, but they're still aviation regulations. So, the answer to this varies a lot by location.

What do you mean by "unsafe airline"? Do you mean an airline which is forbidden to use a national airspace?

Global
Starting from the top, we find the International Civil Aviation Organisation (ICAO), which is a United Nations agency. ICAO was formed in 1944 when the Chicago Convention was signed, and initially had 52 member states. Today, 191 states worldwide are members of ICAO. The headquarter is in Montreal, Canada, and there are 7 regional offices.
ICAO standards and other provisions are developed in the following forms:
Standards and Recommended Practises (SARPs):
Technical specifications adopted by the Council of ICAO in order to achieve the highest practicable degree of uniformity in regulations, standards, procedures and organization within air navigation. Member states will conform to standards and will endeavour to conform to recommended practises. States are invited to inform ICAO of non-compliance.
Procedures for Air Navigation Services (PANS)
PANS comprise operating practises and material too detailed for SARPs. They are suitable for application on a worldwide basis. Member states are invited to publish differences between national procedures when considered important in the interest of safety.
Regional Supplementary Procedures (SUPPs)
SUPPs are supplementary procedures which are only valid within one of the ICAO regional office regions. For example, there are supplementary procedures published only valid within the European/North Atlantic region.
Also worth mentioning are the International Telecommunication Union (ITU) and the World Meteorological Organization (WMO), both of which function on an (almost) global level.
Regional
Below ICAO we have regional organisations. As an example, in Europe, the European Union (EU) provides legislations for its member states. Non-regulatory organisations, such as the European Aviation Safety Agency (EASA), assist the EU in developing regulations (but the EU, not EASA, is the regulatory authority).
Some areas do not have regional regulators like the EU. In such areas, national regulations are handled directly by national regulators. Within the EU, countries also have national regulators – but they are bound to base their regulations on EU regulations.
National
Below the regional level we have national regulators, commonly referred to as civil aviation administrations (CAA). Each country will have their own CAA. One that you will often hear about is the Federal Aviation Administration (FAA), which is the national regulator in the USA.
Generally speaking, a national regulator will be following framework regulations published by the national ministry of transport. The term ministry of transport is also sometimes applied to the departments or other government agencies administering transport in nations who do not employ ministers. The framework regulations from the ministry of transport are largely based on ICAO SARPs, PANS, SUPPs and any regional regulations (such as EU regulations).
The national regulator will publish detailed regulations, which are adapted by the air navigation service providers, as well as airlines, pilots, air traffic controllers, maintainence companies etc. etc.
The service providers, commonly referred to as ANSPs, are the organisations actually providing air navigation services, such as communication, navigation and surveillance equipment, meteorological services, air traffic management (including ATC), aeronautical information and search and rescue. Most ANSPs operate within a single nation, but there are also multinational ANSPs, a few examples are ASCENA (Africa and Madagascar), COCESNA (Central America), EUROCONTROL (Benelux) and NUAC (Sweden and Denmark).
The service providers work together with the national regulators to develop detailed procedures, but do not (usually) have any regulatory authority.

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text:
How much force can the Dukane DK 100 ULB (Underwater Locator Beacon) widthstand?
How much shock (force) can this beacon withstand on impact?
Is there an FAA certification telling us anything about it?

It seems to be behind a paywall. The manufacturer says it complies with TSO-C121b, which says that it complies with SAE AS8045A. SAE wants USD 74 for the document.

"The rules governing underwater locator beacons are the Federal Aviation Administration (FAA) TSO-C121, C121a, and C121b. European Aviation Safety Agency (EASA) is expected to publish ETSO requirements that parallel the FAA standards." (Source). C121b extends the life to 90 days. CVR themselves are tested at 3,400 G (6.5 ms, half-sine shock wave), the ULB must at least sustain this.


text:
Was there ever an accident from in-flight smoking?
In the 80s and 90s, regulation increased to prohibit smoking in passenger planes. Was smoking ever identified as the cause for serious accident in flight (for example the cabin caught fire as a result of a stray cigarette on the carpeting or seats)?

As a side note, smoking was banned for health reasons, not flight safety reasons. (Barring the fact that a cigarette started in-flight fire would likely be unhealthy for all.)

Why would someone downvote this question?

Related question: Was smoking banned because of passenger safety or occupational safety?.

This comment on another answer is relevant.

24 December 1982; CAAC Ilyushin 18B; Canton (Guangzhou), China: The aircraft was on a scheduled domestic flight when an onboard fire broke out as a result of a carelessly discarded cigarette. The aircraft landed and the passengers and crew evacuated, but 25 of the 50 passengers were killed. All 11 crew members survived. source

The cause of the accident of a DH 86 Express on 2 October 1935 is not confirmed, but likely caused by a cigarette, albeit indirectly. From the Wikipedia article on the DH 86:

On 2 October 1935 Holyman's VH-URT Loina was also lost in Bass Strait,
  again with no survivors. This time a significant amount of wreckage
  was recovered from the sea and from beaches on Flinders Island.
  Investigation of the wreckage revealed a section of charred carpet on
  a piece of cabin flooring from just ahead of the lavatory door. It was
  thought possible that a small fire from a dropped cigarette had led to
  someone running aft suddenly to stamp it out – the sort of sudden
  change in weight distribution that could set up a fatal loss of
  directional control while the aircraft was on a low-speed landing
  approach.


text:
What exactly is trim?
Although I have a rough idea of what it is...
In my mind from growing up watching hundreds of hours of Seconds from Disaster / Air Crash Investigation, trimming an aircraft is turning a dial that changes the airplanes "forward" direction. So maybe it changes the control surfaces so that the plane is flying straight forward even though the rudder for example is at some deflection angle that isn't 0.
However if I was asked to define trim I couldn't exactly say what it is, what situations I would use it for or how it's achieved.

If the aircraft is trimmed, the flight controls are in a state where no force needs to be exerted in order to continue straight and level flight. Aerodynamic and gravitational moments about all three axes are nulled out.
Changing the trim of the aircraft in pitch could happen in the following ways:

a shift in centre of gravity, for instance by shifting fuel from centre tanks to tail tanks, or payload shifting position;
a change in thrust of an engine that is located above or below the centre of gravity;
a change in horizontal tail angle or trim tab;
a deflection of the elevator.

If the aircraft was in straight and level flight and the trim changes because of a change in any of the above, it can be compensated for by the other factors. Elevator deflection is fastest but requires a pilot force which is uncomfortable for longer periods, that is why the forces can be trimmed out to make the new stick position the neutral force one.

Trim is the control that adjusts the trim tab.
Effectively its a way to fine tune/change the control surface to elevate control forces. Since airplanes can be loaded differently and the Center Of Gravity moves as the aircraft burns fuel the control surfaces must be slightly adjusted for each flight/flight segment to achieve straight and level flight for a given configuration/load.
Wiki gives a nice description of it, this is for elevator control but the same applies for all control surface trim.

Elevator trim frees the pilot from exerting constant pressure on the
  pitch controls. Instead, the pilot adjusts a longitudinal trim control
  (often in the form of a wheel) to cancel out control forces for a
  given airspeed / weight distribution. Typically, when this trim
  control (wheel or lever) is rotated or moved forward, the nose is held
  down; conversely, if the trim control is moved back, the tail becomes
  "heavy". Many newer aircraft, especially jet aircraft, have electric
  trim controls.

There is a nice article on it here as well as here

what situations I would use it for or how it's achieved.

The trim is generally adjusted any time the aircraft transitions flight phase (climb to cruise, cruise to decent etc) or when the power setting is changed or periodically in cruise if the CG is greatly effected. For example if you climb out at full power, reach your cruising altitude of 3000 ft. push the nose over and pull the power back to your cruise power setting you may find you are still applying forward control pressure to keep the airplane from climbing. In this case you would trim off the control pressure by rolling the wheel forward until you no longer needed to apply control pressure to keep the plane level. At this point you could fly "hands off".


text:
Why weren't the Airbus A330 engines designed with a system to stop their fans?
Why wasn't the Airbus A330 designed to stop its fans (with some kind of 'handbrake')?
To clarify, I am specifically talking about the aircraft that flew Air Asia flight D7237.
During the flight the aircraft suffered from a fan blade separation event and the the result was that the engine became unbalanced.
This was the result of the incident the plane was able to continue flying for over an hour and a half with the "moderate" vibrations and able to land safely (where the passengers were rewarded with a $20 voucher)
It's my understanding that the engine was immediately shut down, and that the cause of the vibrations was the fanblades freely turning as the plane moved very fast through the air (similar to blowing very hard into a turned off household fan)
But to me, it seems the whole situation could have been avoided if there was simply some kind of "brake" or 'locking' feature that prevented the fanblades from turning freely in the wind.
I feel as though there wouldn't exist another scenario where a plane could possibly experience more severe, prolonged vibrations than a windmilling event, and the windmilling event itself could be prevented if there was simply a way to lock the fanblades from moving freely.
The reason I say A330s in particular is because I am not aware of the features of every other jetliner, although I am aware some propeller engines can feather their blade parallel to the direction of airflow to prevent this.

Weight, extra maintenance, low probability of actually using such a ststem...a long list of reasons exists as to why such a system was not implemented.

As you can see, windmilling did not impact the overall safety of the flight. Why add weight and cost for something that isn't needed?

@GdD I would assume that the plane was built to the specification to resist windmilling. The question I am asking is, why was it built to resist windmilling (making sure every joint is strong and sturdy enough etc) instead of a 'simple' mechanism to halt fan blade movement. I say that on the assumption that the most violent vibrations a plane can expect to recieve in any 'incident' would be from windmilling (i may be wrong)

humorous alternative interpretation of the title when reading it on the hot network questions list:  "Why wasn't the Airbus A330 designed to stop people who really like it?"

You'd also have to account for the break/locking device failing itself, which would be bad to happen inflight.

You are probably underestimating what it would take to "stop" the fans by a large degree, but aside from that, the amount of drag caused by a "stopped" fan is very much bigger than a fan that is windmilling. The default scenario for ETOPS flights after an engine failure is that the failed engine will continue to windmill, and a lot of engine design work is done to try to make sure that will happen. That said, there has been at least one incident on a 747 where a failed engine did stop windmilling - but losing one engine out of four is less of a problem than losing one out of two.

There was an infamous incident with a 747 freighter flying from the far east to the UK (IIRC) where an engine failure caused vibration levels that annoyed the crew. So they made an unscheduled landing somewhere in the third world, and fixed the problem themselves by restraining the fan blades with the webbing used to hold down the cargo(!!!) That worked fine, except the increased drag meant they didn't have enough fuel to complete the flight, so they decided to make another unscheduled stop in Germany to refuel. The German ground crew took one look at the webbing, and impounded the plane...

@alephzero do you have a reference for this story?

@Ksery: Perhaps because the strength needed to resist vibration from a windmilling engine is also useful in resisting vibrations from other causes such as turbulence, which are far more commonly encountered.  Whereas an anti-windmilling device is only useful on rare occasions.

@Thomas: German here; I can't give a reference for that, but at least the part of Germany of what alephzero told, sounds legit. No one would let that bird takeoff over here and it really made me laugh to read that '^.^

@alephzero - I think I found that story (with pictures) at Snopes, but they discredited it as an urban legend. Their story is a bit different in that it's said to be a Chinese passenger airline on a revenue flight, but has has enough similarities (the damaged blades were strapped with seatbelts, and the flight stopped in Frankfurt to refuel due to increased fuel consumption where it was grounded) to make me think it's the same story.

Aren't blocked blades essentially a huge airbrake? Also, imagine the torque at the axis, where the brake likely would be.

Based on general engineering principles, there are multiple reasons why such a locking device could be unhelpful at best, and dangerous at worst:

It would be one more system that adds weight and complexity.
It would take up additional room that isn't available, and making that room would affect the aerodynamics and the weight.
It would be one more system to check and maintain.
If it fails, does it fail in a way that causes a running engine to stop, thus creating a dangerous situation, or does it fail in a way that makes it no better than not having it at all?
Is it more reliable than the jet engine?
There are situations where windmilling is desirable, turning engaging the brake into one more thing the pilots have to decide to do. Is it worth the cognitive load on the pilots?

Engine failures of any kind are rare, and, as was the case with this incident, often quite survivable. It's not worth the design cost, material cost, weight cost, maintenance cost, or training cost to have a turbine locking device.
In this case, the only thing that a brake would have accomplished is reduction in vibration. With one out of two of the engines down, the pilots would still have brought the airplane in for an early landing, and not continued on to their planned destination.
While this flight was not under US jurisdiction, the Rolls Royce Trent 700 engines used on the aircraft still have to comply with FAA regulations, if for no other reason than that A330 aircraft are flown in the United States. In particular, 14 CFR Part 33 is titled "Airworthiness Standards: Aircraft Engines", and says the following in §33.74 Continued rotation:

If any of the engine main rotating systems continue to rotate after the engine is shutdown for any reason while in flight, and if means to prevent that continued rotation are not provided, then any continued rotation during the maximum period of flight, and in the flight conditions expected to occur with that engine inoperative, may not result in any condition described in §33.75(g)(2)(i) through (vi) of this part.

The points described in §33.75(g)(2)(i) through (vi) are:

(i) Non-containment of high-energy debris;
(ii) Concentration of toxic products in the engine bleed air intended for the cabin sufficient to incapacitate crew or passengers;
(iii) Significant thrust in the opposite direction to that commanded by the pilot;
(iv) Uncontrolled fire;
(v) Failure of the engine mount system leading to inadvertent engine separation;
(vi) Release of the propeller by the engine, if applicable;

Since I can not find any documentation to show that the Trent 700 has a rotor locking device, it must be designed to meet these regulations. Vibration is not listed as one of the hazardous conditions. It is true that vibration can be hazardous, but that's more for a running engine, and vibration monitoring systems exist to shut a malfunctioning engine down.
Other regulatory bodies no doubt have similar requirements. I picked the FAA since it is the one I am most familiar with.

"There are situations where windmilling is desirable", what conditions might that be?

@Ksery Windmilling is one way to restart a failed engine in flight if you don't have bleed air available.

@Ksery Under certain circumstances, it's possible to windmill start a stopped turbine engine, similar to push-starting a car. In the case under discussion, you can't and don't want to do that, but in emergency situations where it doesn't look like there's engine damage, you might want to give it a shot. See Does windmill restart often work for airliner engines?

" Significant thrust in the opposite direction to that commanded by the pilot;" Am i correct in reading that its possible for an engine to produce thrust out of the front?

@Ksery For a jet, not out the front, no. Thrust reversers deflect gases from the rear. For a prop plane, some propellers have variable-pitch blades that can be rotated to produce reverse thrust.

Yes propellers can feather, a feature which is required for delivering thrust over a wide range of airspeeds. Fixed blade propellers had a problem with either delivering good take-off thrust, or limiting the maximum speed of the aircraft. Variable pitch propellers were invented before WW2 and widely implemented because of the limitations of fixed blade props.
Turbofans have a fan disk imside a shroud, which decelerates the air before it hits the fan blades. This setup can be optimised for cruise comditions, and still delivers good takeoff thrust. The jet engine core delivers part of the take-off thrust directly. The fan is fixed pitch because it can be - a variable pitch mechanism, or a brake for that matter, adds cost and complexity. Most present day airliners have these engines, including the A330.
However, the larger the fan in a bypass turbofan, the more efficient it is, and a large fixed pitch fan starts to have the same issues as a fixed pitch propeller. So now large bypass variable pitch turbofans are being developed, for instance the Rolls Royce Ultrafan.

The variable pitch fan is actually not a new idea, Turbomeca developed the Astafan in the 1960s.
Windwilling of any fan, variable pitch or not, is not bad per se:

A windmilling engine can be restarted, priority 1 in an undamaged engine.
Windmilling engines have less drag than non-rotating engines, and less asymmetric thrust of the remaining engine(s) to trim away.

If it can be demonstrated that a windmilling engine with a broken fan blade only causes mild discomfort and no further catastrophies, and that the incidence is very rare, then there is no actual problem to solve.

This questions answers have some interesting facts regarding fixed propellars at high speed https://aviation.stackexchange.com/questions/38429/why-were-the-speed-records-set-by-seaplanes-in-the-early-thirties


text:
Why is the temperature of the cabin so low during a flight?
While I understand that at very high altitudes the ambient air temperature is extremely cold outside the aircraft (-56 F), it always bothers me that I find myself sneezing and genuinely uncomfortable once I'm about 30 minutes into my flight.
The question I am specifically asking is, why is the chosen temperature inside the cabin low as opposed to high? Surely it could be set a few degrees higher to a "warmer" temperature?

Have you looked for any information on this subject? A quick search turns up lots of reading material. Perhaps you could make your question more specifically applicable to available information.

Thanks for the link, very Interesting... I was not actually aware the cabin crew could adjust the temperature of the cabin, almost every flight I've ever been on (in the 10's) has been extremely cold, and they have all been on different airlines. I assumed this was due to way the air-con worked on airliners

Typically the cabin temperature can be changed and is at the discretion of the Purser (Chief Flight Attendant). Also, generally speaking it's easier for those who are cold to get warm using blankets, but there is no such remedy for those who are hot. Do you really want the cabin temp turned up so that fat old men who heat up with all their personal insulation start taking their shirts off. Aslo, while the passengers may be sitting down, the flight attendants are working their asses off, and for male flight attendants carriers often have a rule that they must wear t-shirts. Foolish rule IMHO.

I actually prefer it cooler, as I get very sweaty as it is on long flights.  I think airlines can cater to all preferences best by keeping it cooler -- if you are cold you can put something on; the reverse doesn't work.

@Terry Sorry for misunderstanding but what is it you find foolish about the male attendants having to wear t-shirts?

@Ksery Just my opinion, but the airline I retired out of had that rule, which meant male flight attendants were dressed unnecessarily warm in the hot, humid summers of the east coast, in the heat of the middle east and the heat of Africa, India, Indonesia, etc. We were a "low cost" carrier, so it was not like we were carrying upscale pax. And certainly the old men who would take off their shirts for their prayers on the Tel Aviv flights certainly didn't care. The unfairness, again IMHO, was that the airline didn't enforce that rule for pilots, and few of us wore t-shirts in the heat.

@Terry I believe he means undershirts that are half sleeve, thus adding an extra layer of clothing to exacerbate the heat. They are often worn in hot environments to stave off sweating (and sweat marks).

Voting to  close as opinion based, since in many hundreds of flights, I've never been too cold.

@Simon I think the question is valid. I've always remember flights as being cold since childhood. I always wish they'd just turn up the temperature 1~2 C.

@kevin But then I would be too warm.  You say "too cold", I say "too warm".  There is no "correct" temperature, therefore, it can only be opinion.

To prevent closure or reopen, you may change your question into How is the temperature selected in the cabin? and whether there are different policies among airlines (if not already answered elsewhere). Just for information, on most airliners air doesn't come directly from the outdoor, but is tapped at some stage of the engines, where it is compressed and very hot. It is then cooled and the temperature is adjusted by mixing with hot air, again from the engines, and air from the cabin. So in the end it is more costly (more fuel) to produce cold air than warm air.

I think this question would be a better fit for travel.se. It's about CAT from the point of view of a passenger, and it's entirely a matter of policy, nothing to do with the flying itself.

I'm voting to close this question as off-topic because it is about commercial air transport from a passenger point-of-view.

On the 737, I can make the cabin as hot as I want to; the challenge is more often adequate cooling if the aircraft got hot on the ground. With the insulation that the aircraft has, the generated heat of 100+ people in a confined space overwhelms the cooling of the outside air. (Yeah, it's utterly counter-intuitive, and I can't explain the why, but that is the way it goes. With the loss of all bleed air, the cabin will get hot -- although that's at 10,000', where you descended after the depressurization.)
I've never been told to run the temperature hot or cold as a fuel-saving measure. In theory, you save a little gas by not running the AC packs in "High", but again, that's mostly used to get more cooling air. Or to quickly warm a jet that sat unheated all night in freezing temperatures.
If the cabin was unbearably cold on a particular flight, somebody just wasn't attentive to the temperature. On any modern airliner, we have the tools to warm things up. Maybe the flight attendants prefered a cold cabin & had sweaters to wear; maybe "really cold" to the OP is actually pretty comfortable to others; maybe the thermostat was indicating erroneously high temperature in the cabin so the automatic system kept putting out cold air; or, maybe the pilots were being jerks and "freezing out" the flight attendants (and passengers) for some reason. Unlikely, that last, but not impossible or unheard of.
As far as a preference to run slightly warm or cool, cool will generally win, simply because warm tends to make airsickness worse, while cool has the opposite effect. On a bumpy flight, the last thing you want is a warm cabin; the saying goes that "popsicles don't puke," and it is accurate.

+1 for "popsicles don't puke". I'm going to remember that!

I feel with you. I have the same problem and actually take ski underwear with me for intercontinental flights. Makes you look foolish when standing in line at some terminal in tropical latitudes …
Cabin air is bled off the engine's compressor and first ducted through a heat exchanger to cool it down. It then is mixed with hot bleed air to adjust its temperature and humidified as desired. Then it enters the cabin through grilles in the ceiling and removed by further grilles near the floor.
As you can imagine, the engine loses some thrust when it is robbed of the air it would normally use to propel the aircraft forward. Therefore, in order to save fuel, cheap (= all) airlines try to reduce bleed as much as they can. In consequence, the heat entering the cabin by means of fresh bleed air is limited, while the outside air cools the whole cabin down continuously. After all, you sit in a tin can, the outside of which is flushed with super cold air at Mach 0.8!


text:
How can I consider a UAV thrust power for wind effects?
Sorry that I can't write English well.
I was wondering how can I consider a UAV thrust power for wind effects.
Assuming a wind velocity of -7 m/s, uav velocity of 10m/s and the stall speed is 10 m/s.
Considering that the desired velocity of the uav must be close to the stall speed. And, assuming that the wind is opposite to the flight direction.
With this information the uav velocity should be 3m/s? And if that's the case, how can I calculate the thrust force.
I'll add a figure and clarifying question.
first, I desire minimize thrust power of UAV for flight.

Like a figure, If the wind speed is 7m/s and the UAV speed is 10 m/s, ground speed must be 3m/s.
however, I thought relative velocity for a UAV is 17m/s. And To minimize thrust, The UAV closed to the stall speed(stall speed is 10m/s).
I thought the UAV need only UAV speed over than 3m/s.
And if that's the case, how can I calculate the thrust force.

There is a very good question about indicated air speed vs true air speed on here somewhere that I think will help you a lot. Essentially it matters what you're speed is relative to.

@mins I think the wind one is the primary.

Related and also related

Your English is better than some native speakers I know ;)

Check this page http://aviation.stackexchange.com/questions/31245/how-is-tas-affected-by-wind/31247?newreg=3723785f31904034aa38e1c2ee1694d7

A useful thing to remember is that the aircraft does not know, or care, how fast it is moving over the ground.  Imagine you could somehow make the Earth disappear but leaving everything else at it is.  The aircraft would still fly perfectly happily.

@min I seem to understand the 'true airspeed'. I thought headwind is help to lift of a UAV so that required thrust for level flight is minimized. Thanks a lot.

As i understand your image:

$V_{uav}$ is the velocity of the plane relative to the air.
$V_{wind}$ is the velocity of the air relative to the ground.
$V_{ground}$ is the velocity of the plane relative to the ground.

If the UAV velocity is 10 m/s and the stall speed is 10 m/s the plane is at its limit of flying no matter what the wind speed is (neglecting turbulences). The relative speed of the plane and the air is crucial, this speed is mandatory for the physics beyond the lift.
There is simple equation how to calculate sum velocities. Note that they are vectors (speed and direction) not just numbers. $V_{wind}$ can be named as drift velocity.
$$\overrightarrow V_{ground}=\overrightarrow V_{uav}+\overrightarrow V_{wind}$$
If the wind direction is opposite to the plane direction its ground speed, at the stall limit, is smaller than the UAV limit. It can be zero (the plane seems stand still) or even negative (plane seems to reverse).
Side notes: $V_{uav}$ is The velocity a pilot cares the most, $V_{ground}$ is the velocity his manager cares. This wind effect is also the reason why flying wit tailwind is preferred by airlines - they spare fuel - and it is also the reason why takeoff and landing is preferred in headwind - you need shorter runway to start/land sucesfully. With tailwind the runway may not be long enough.

Thanks for your answer .
If the plane reduce fuel consuming. (takeoff and landing in headwind)
Would please recommend paper or reference for Thrust power of a plane in wind effects?

Thrust required is going to involve a lot more than airspeed, stallspeed and the speed of the headwind. It deals a lot with the coefficient of drag and the coefficient of lift as well as the weight.
$T=\frac{W}{(Cl/Cd)}$
where $T$ is thrust, $W$ is weight, $Cl$ is coefficient of lift and $Cd$ is coefficient of drag.
You can find lift and drag data for the wing you will be using on airfoiltools.com, but finding the overall lift and drag of the aircraft will require actual experimental testing.
You say that you want to minimize your thrust required to get to speed, so you will want to operate at $Cl/Cd$ max, which is the most efficient way of flying anyway.
here's a useful formula to figure Cl.
$L = Cl(dv^2/2)A$
where $L$ is lift (you can substitute your weight here)
$d$ is air density, $v$ is velocity and $A$ is wing area


text:
What is meant by "fuel flow: on " in checklists?
What is mean by "fuel flow: on " in checklists? For example:
http://www.projectlear45.nl/docs/Checklist_LEAR45.pdf

I looked at the checklist.  If I didn't know better I would assume  it meant "fuel flow: cutoff" in the pre-start checklist means no fuel to the engine; engine better be off.  In the startup checklist "fuel flow: on" would mean give the engine some fuel so you can start the engine.   How long you been flying Lear may I ask?

@user6035379 considering that checklist is a flightsim one (unless ctrl+shift+f4 is a thing in learjets) I suspect the answer to your question is "oh, donkey's years - in flight sim" :)

@user6035379 Thank you for the answer. I myself have not been flying learjet except of simulators.

@Jamiec : get a badge for knowing what checklist I looked at and yeah ... donkey..

In the real aircraft that checklist item would mean bringing the thrust lever of the engine to be started up out of cutoff and to the idle position. This would be accomplished by physically moving the thrust lever forward slightly out of the cutoff detent.
However, in the computer flight sim for which the linked checklist provides guidance, the cutoff position of the thrust levers is not simulated. Instead, thrust lever positions below idle command reverse thrust. For this reason, the checklist calls for using the computer keystroke ctrl-shift-F4 to command fuel flow on. This keystroke combination commands mixture full rich in simulated piston aircraft.
In the real Lear 45, fuel flow and scheduling during start is controlled by the Digital Electronic Engine Control (DEEC). For this reason, the start checklist calls for setting the appropriate thrust lever to idle prior to commanding engine spool up in preparation for the DEEC to automatically start actual fuel flow once the appropriate compressor speed is achieved.
It is worth noting that after initially setting the thrust lever to idle—or hitting ctrl-shift-F4 on your computer—the fuel flow indication should read zero. The check for appropriate positive fuel flow comes later in the start sequence.
Compared to setting the thrust lever to idle in the Lear 45, the analogous control command for starting most piston engines would be mixture to full rich and for most turboprop aircraft would be fuel condition lever to low idle or similar.


text:
Is this really a British Airways 727?
I came upon this clip on YouTube this week:

It appears to depict a Boeing 727 in British Airways livery. My first thought was that it's a Trident, but it is definitely a B727. I was a regular visitor to Heathrow and Gatwick in the 70s and 80s in my plane spotting days and I don't remember BA ever operating 727s.
So, how did this 727 come to be painted in BA colours?
Bonus question: which airport was this filmed at, since it's not either of the two main London airports?

Hmm... Interestingly, the wiki pages for BA, BOAC, and BEA don't seem to mention the 727 being used anywhere. BEA did try to order 727s, but the British government didn't allow it and forced them to buy British aircraft instead. Perhaps this is from when they were evaluating the 727?

It's probably operated by Comair, you can find more pictures on airliners.net, and even in newer livery.

@reirab I wondered about that but BEA's dalliance with the 727 occurred in the 60s, long before British Airways came into existence in 1974.

BA took over Dan Air's 7x 727s when they bought the airline in early 90s. They had 727s at gatwick

Interesting question!
In the background, a Lufthansa Boeing 747-400 can be seen. Therefore, I assume the airport is a Lufthansa destination. Since the 727 is not exactly a long range aircraft, but the 747 is, my first thought would be that the airport is in Germany.
I couldn't really see what livery the 737-200 in front of the LH 747 was, but soon in the take-off roll (0:10 seconds) a propeller aircraft (Dash 8?) with a South African Airlines tail appears. Then during the rest of the video many SAA tails are visible and also a number orange tails. I needed to get my first aircraft book (printed 1989) to discover that the old livery of SAA featured an orange tail.
It is thus pretty safe to assume that the airport is in South Africa.
That makes it quite rare for a British Airways 727 to appear there. The range of the aircraft is approximately 2000 nautical miles which is a bit short of the almost 5000 nautical miles that London - Johannesburg measures.
I then remembered a recent accident in South Africa involving a Comair Boeing 737-400 in British Airways livery. This led me to believe that this particular Boeing 727 in the video may be a Comair 727 in BA livery too.
A little search turned up this picture on airliners.net, confirming that Comair indeed operated the 727 in BA livery.

The airport is O.R. Tambo in Johannesburg:

A still from the youtube video showing some buildings in the background

The same buildings in Google Maps

That is some excellent deduction work Sherlock!

Thank you! The Comair page on Wikipedia confirms the link to BA, but doesn't give a date when the arrangement started. The coat-of-arms livery dates this clip to post-1984, but I imagine things had been in place a while by then.

Gah! There's a ghost 747 on the ramp!

Simply brilliant!

@Airsick, I expect this to be late 1990s. SAA introduced their new livery in 1997 and in the video they are cleary in the middle of the transformation.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the RNP requirement within the KZAK FIR?
What's the RNP requirement with KZAK FIR?
I thought it is RNP 10 operating in NOPAC AND PACOTS, but I am not sure.

Related: ICAO - Overview of Oceanic and Continental Remote Navigation Specifications. RNAV-10 prescribed, RNP-4 optional (and no authorization required).

To be exact RNAV 10 is required when operating in the KZAK FIR. This enables 50NM longitudinal and lateral separation between aircrafts.
Unfortunately, the requirement might be designated RNP 10 due to legacy reasons. The difference between RNAV and RNP is that RNAV requires no onboard performance monitoring and alerting capability, while, among other things, RNP does.
RNP 4 is optional to allow closer 30NM longitudinal and lateral separation between RNP 4 capable/authorized aircraft thus increasing the airspace capacity.
Sources:

ICAO Doc 9613 - Performance-based Navigation (PBN) Manual
ICAO Doc 8168 - Procedures for Air Navigation Services — Aircraft Operations, Volume I (PANS-OPS Vol I)


text:
What does "POS ITERV WAS CHGD" mean on the ACARS page of a Boeing 737?
During the whole flight, the message "POS ITERV WAS CHGD" appeared frequently on the ACARS page of the MCDU (Multipurpose Control and Display Unit). The aircraft is a Boeing 737.  I cannot find any reference in the FCOM (Flight Crew Operating Manual).
What does this message mean and why does it appear?

Hello gordongly, welcome to Aviation.stackexchange. In the future, please don't use ALL CAPITALS in the title and body of your question, it comes accross as shouting.

Where did you fly? Do you have ADS-C or CPDLC active?

China, i think not

I suspect this to mean that the interval of ADS-C position reports has been changed. All pages mentioning this message that I can find online are in Chinese, so it seems to be something specific to the ADS-C usage there.

No no I saw these webpage you mentioned.

Assuming it's the real aircraft (doesn't look like a sim), can't your airline ask Boeing through some channel? I always find it odd for RL pilots to ask aircraft-specific questions on the internet

@Ectric which point...? You are probably right :-)

@ElEctric I probably did not miss the point entirely. See answer.

Your aircraft is reporting its position periodically over the Aircraft Communications Addressing and Reporting System (ACARS) to the airline operations centre (AOC).
Since there are costs related to sending these position messages, the interval in which these message are sent drives operating costs for the airline.
This patent from China Southern Airlines (original Chinese version here) describes the behaviour you have observed on the MCDU. Apparently it allows the AOC to change the position reporting interval over ACARS remotely. If the interval is changed, a "POS ITERV WAS CHGD" text is displayed on the MCDU scratch pad.
The relevant text from the patent (including translation & typesetting errors):

...
[0087] PTIC message display unit, see FIG. 6, the module receives PTIC
  PTIC uplink triggering instruction, parsing PTIC variable, position
  determined by the adjusted multicast time interval T3, if the variable
  is valid PTIC, is given in M⑶U unit tip text message to inform the
  crew of the current position of the broadcast time interval has been
  changed, the present invention uses "P〇S ITERV wAS CHGD" text gives
  the unit prompts; the message is always displayed in MCUD the scratch
  area (Scratchpad) until a new the message will disappear after replace
  the unit or manually pressing CLR keyboard. ...

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
How to interpret 14 CFR Part 61 Requirements 61.129 on instrument training time?
For part (3)

(i) - Ten hours of instrument training using a view-limiting device including attitude instrument flying, partial panel skills, recovery from unusual flight attitudes, and intercepting and tracking navigational systems. Five hours of the 10 hours required on instrument training must be in a single engine airplane;

Can this time be previous instrument time, or does it have to be specific to the commercial certificate?
Same thing with the night take off and landings at a towered airport.

(4)(ii) 5 hours in night VFR conditions with 10 takeoffs and 10 landings (with each landing involving a flight in the traffic pattern) at an airport with an operating control tower.

Your first question has already been answered here

The experience requirement for a commercial rating need not be acquired during training for a commercial rating.


text:
Do controllers take wind into account when giving headings?
When ATC gives you headings to fly, do they consider wind correction? In theory they should because they call it a heading and not a track, but do they? After all, the heading they want you to fly depends on wind direction and airspeed.
Or do they actually mean track instead of heading?

When the controller says heading, he means heading.
So if he wants you to go into a specific direction, he will take wind into account. The reason for issuing heading are:

Every aircraft can fly it, because a compass is fitted on every aircraft. Track keeping requires more sophisticated avionics.
If two aircraft fly adjacent to each other, the wind will offset them by the same amount and therefore separation is assured.

Quite often a controller will ask you to report your present heading prior to instructing a one so he can make more accurate adjustments to your course, especially if you were under own navigation before being vectored.
With Mode S radars and the right equipment in the aircraft, the current heading can be downloaded from the avionics without the pilot being aware of it.

#2 is not entirely true. When there's a significant crosswind, an aircraft flying a heading of 200 at 100kts will have a different track than an aircraft flying the same heading at 200kts

That is true, but in such a situation the separation issue will be resolved longitudinally before it becomes a problem laterally.

Still, I wonder if a controller will provide the correct heading to a light airplane flying at 90kts with a 60kt crosswind (which is not that uncommon above 3000ft)

They'll certainly try! I've never heard a controller provide a track to be flown.

@PhilippeLeybaert -- (not sure why I just happened to stumble across this) -- re your comment-- well, it's complicated. Yes, the ground tracks are different.  Yet from the airmass reference frame the direction of travel is the same-- so it is absolutely valid to say that separation is assured. There is no possibility that the aircraft will ever get closer together than the shortest distance you could measure between each of their air track lines, meaning an imaginary line drawn from nose to tail of each individual airplane, and extended infinitely far in each direction, fore and aft.

The "air track" line of one plane is parallel to the air track line of the other, and the shortest distance between those two lines is the closest the planes could ever get, even though the ground track lines are not parallel.  (A bit of mind-bender...)

ATC gives headings, and they mean heading; any wind correction is included in the controller's planning. You'll occasionally hear controllers adjust headings ("turn 10 degrees left") because the wind exceeded their expectations.


text:
What are the risks involved when doing a classic zero-g maneuver?
I suspect most pilots have done it at least once: briefly experience zero g when flying a parabolic path. It's quite an experience (if your stomach can handle it).
Question is: are there any risks involved in doing something like that? (I know, getting in an airplane by itself is a risk, but that's not the point)
I could think of a few potential risks, but I'm not sure if they are real or not:

Engine lubrication in single engine piston airplanes

And if not properly executed:

Risk of a stall, both in the pull up phase and in the "arc" phase
Overstressing the airplane when pulling out of the dive to get up to speed

Follow-up questions: Is it considered to be an acrobatic maneuver? Are there any regulations that would prohibit it?

Fuel starvation also comes to mind....  Also, the aerobatic question is answered here: http://aviation.stackexchange.com/questions/307/what-are-the-us-definition-and-restrictions-on-aerobatic-flight

any mechanism that is gravity powered or relies on gravity to work properly  will not work anymore, one of those is bubbles in hydraulics because the reservoir has some air in it and that may get sucked up during the 0G time

Why does the engine lubrication argument specifically applies to single engine piston airplanes? Isn't gravity based lubrication used on multi engine airplanes / turbine engines?

@DeltaLima I don't know, hence the question :-)

@delta lima: You are correct that the lubrication argument does NOT apply exclusively to single engine aircraft.  Acrobatic aircraft have inverted fuel and lubrication systems.  This allows the engines to run inverted.  Typically larger aircraft (twins, etc) are not built for acro flight and therefore the engines don't have these systems.  I presume the same is true for the turbine engines, but I have no experience with those.

@ratchetfreak - I think having bubbles in hydraulics is a severe problem anyways, independent of where it is. A reservoir is needed to handle thermal expansion.

@VolkerSiegel but a container partially filled with gas can be enough to create that expansion capability. If the intake into the compressor is submerged then it won't add airbubbles into the liquid. Valves on the outlet back into the reservoir will avoid the compressibility issues at the working end.

@ratchetfreak You are right, there can be air in the reservoir where the pump gets the hydraulic fluid, I was wrong implying it is not possible to have air somewhere in the system. But I was actually right regarding that air circulating in the active part of the system is a problem, and a surprisingly bad one. It does not only make the system behave somewhat soft like pneumatics, hydraulics is reacting "hard". See a backhoe, especially if it shakes the spoon to remove dirt. But air causes cavitation in the system, actually material inside. It is collapsing bubbles so hard they can emit light.

The biggest risk is improper execution.  If you build up too much airspeed and pull out of the dive at 4-G and break something, that will be your primary issue.
Your secondary risks will be associated with the fuel and oil system starvation if they depend on gravity for operation.  This risk is balanced by how long you can sustain 0-g flight.  Oil issues are bigger risk than fuel, as even if you did sustain 0-g long enough to starve the engine, you should get it back as soon as you are in positive G.  This particular risk will vary by airplane and I probably can't say something as general as "not typically a problem for short duration 0-g excursions".
An additional secondary risk is unsecured objects in the cockpit.  This presents a number of possible complications:

floating objects may distract you from aviating
floating objects may break something (the example of a window in the cockpit would cause a major distraction for the remainder of flight)
Most importantly, this can change your CG which can have dire consequences if something heavy enough gets moved far enough.

I wouldn't put risk of stall too high on the list, because you should be doing this with enough altitude and in coordinated flight so a stall would just be a simple recovery.
As for whether this is an aerobatic maneuver, it is a lot like a departure stall but a botched recovery (pushing over to 0-g before the stall breaks) and only a passenger could say for sure what you were actually doing.
That leads into the last risk I can think of, and that is when your passenger deposits his/her lunch all over the airplane.  In 0-g that could get on the windscreen and obscure your vision.  Be careful!

Floating/flying objects could also be a hazard.  (A flight instructor friend of mine told me about a window that was broken out this way.)

@Lnafziger good point, I'll add that to the answer.

@Lnafziger not to forget dirt etc. Sometimes that makes me sneeze... oh, and another danger would be an improperly secured crew (both to to others and themselves).

I did quite a number of zero gravity manoeuvres on a Cessna Citation II, not as a pilot but as an experiment coordinator.
The engine lubrication was gravity based on that aircraft, and zero-g caused a Master Caution / oil pressure warning. Since the zero gravity manoeuvres lasted only for about 12 seconds, this wasn't a problem according to the engine manufacturer.
Entry and recovery caused extra g-forces on the airframe, I remember we reached 2.5g during pull up. Especially the recovery out of the parabolic flight was tricky, balancing between duration of the zero-g segment, g-force during pull up and overspeed. Sometimes spoilers were deployed at the end of the parabolic section to keep the speed down.
There isn't much risk of stall, since the higher wing loading occurs at quite a high speed, keeping the required lift coefficient low. The low speed segment on top of the parabola is a zero g, so no stalling there.
Another serious risk is getting hit by things flying around the cockpit and cabin when negative G is accidentally achieved. Flight manuals crashing into your head at 2.5g during the pull up are no fun.
Negative G's are also a risk for the fuel system when it is purely gravity based. If air bubbles get trapped inside the fuel line it can cause engine stall. I think this is less of a problem in jet / turbine engines which seem to have fuel pumps in any case.
On the Citation II negative G s caused a spray of fuel from the vents in the wing tip;  spectacular but harmless.

Even airplanes with fuel pumps can have their fuel pick up port uncovered during negative g flight and air can get into the system that way.


text:
How to properly enter a holding pattern?
Once ATC have assigned me a holding pattern, how do I determine where to intercept it?
And once that I have determined the intercept point, how do I proceed?
I have heard about the teardrop and the parallel entries, are there others? How do I select the most appropriate entry?
During the intercept maneuver, can I assume[1] that the appropriate airspace is free (since ATC told me to intercept that hold) or there is high risk of coming close to other aircrafts?

[1] this does not mean that I will not look at the radar/out of the window, is just to know the level of attention that I have to pay to this aspect.

to source from wikipedia:

There are three standard types of entries: direct, parallel, and
  offset (teardrop). The proper entry procedure is determined by the
  angle difference between the direction the aircraft flies to arrive at
  the beacon and the direction of the inbound leg of the holding
  pattern.

A direct entry is performed exactly as it sounds: the aircraft flies directly to the holding fix, and immediately begins the first turn
  outbound.

In a parallel entry, the aircraft flies to the holding fix, parallels the inbound course for one minute outbound, and then turns
  back, flies directly to the fix, and continues in the hold from there.

In an offset or teardrop entry, the aircraft flies to the holding fix, turns into the protected area, flies for one minute, and then
  turns back inbound, proceeds to the fix and continues from there.

As you can see the maneuvers are all inside the area circumscribed by the holding pattern (not counting flying directly to the holding fix) so you can assume the airspace is clear at your altitude.
Important to note is that you should fly directly to the beacon and then reorient yourself as appropriate.
The airport approach charts will indicate where the beacons/landmarks are located, which code they use and which heading the "inbound" leg (when flying towards the beacon) has.

@ratchetfreak Before I retired in 1999, a standard holding pattern entry was recommended but not required. Is that still the case or is a standard entry now mandatory?

@Terry it is still the same AFAIK.  In practice, fly whatever entry you want.

@Federico if the hold isn't published on a chart (approach or IFR enroute) the fix will always be given referenced to a published fix that is most likely already on your route of flight.


text:
Are any special certs or licenses needed for Snow-ski equipped planes?
It has been asked and answered here that the ASEL is for Land operations and ASES for Seaborne. Are there requirements specific to using snow-ski equipped planes?
I am most interested in the US, although discussions of other places is fine.

From the FAA manual:

Title 14 of the Code of Federal Regulations (14 CFR)
  part 61 does not require specific pilot training and
  authorization to operate skiplanes; however, it is
  important to train with a qualified skiplane flight
  instructor.
Since most skiplanes operate in a wide variety of conditions,
  such as landing on frozen or snow-covered
  lakes and sloping glaciers, with varying qualities of
  snow, it is important to know how performance is
  affected. Use the performance data provided by the
  manufacturer.

From looking at 14 CFR part 61, section 61.5 lists the different ratings. While it differentiates sea and land, there is no "ski" category.

How does this apply to landing a seaplane on snow? :) The US Navy used to do it with flying boats, and Kenmore Air in the Pacific Northwest has done it in the past as well!


text:
What are the main differences between Flares and Chaff?
Over the years I've heard the two used almost interchangeably but after watching some videos it would seem that they each have specific and particular functions.

Both chaff and flares are defensive countermeasures deployed by military aircraft. The purpose is to confuse radar-guided or infrared-guided anti-aircraft missiles fired so that they can divert.
A good definition about them is here:

Chaff is composed of millions of tiny aluminum or zinc coated fibers stored on-board the aircraft in tubes. When an aircraft is
threatened by radar tracking missiles, chaff is ejected into the
turbulent wake of air behind the plane.
Flares are used to distract heat-seeking missiles. Most are magnesium pellets ejected from tubes to ignite in the wake behind the
aircraft. These flares burn at temperatures above 2,000 degrees
Fahrenheit, hotter than the jet engine nozzles or exhaust and exhibit
large amounts of infrared light.

Flare
Flares are a, let's call it "passive defense system". They are used for misleading rockets fired on an aircraft. Many missiles are following a heat source to hit their target. In case of an aircraft, it's the engine. If such a missile is on the way, the pilot fires those flares. They burn really hot and the missile will fly into the flare instead of the aircraft.

Source
Chaff
Chaff is also spread out by aircraft. There are used for, what can be called "electronic war". As you know, a radar sends out electromagnetic signals. If they are being reflected to the radar, there is a dot visible on the radar. This can be an aircraft but also lots of birds. Now, chaff is made of aluminium or metallized glass fibre or plastic. So, when the aircraft spreads a big cloud of that chaff, it is visible on the radar. And this can work like a curtain. There is a wall of chaff sprayed out. Behind that wall, every aircraft is invisible and operations can be accomplished secretly.
But chaff can also be used as "flare" but for radar-assisted systems. Like radar-lead missiles or radar-targeting systems by fighters.

Source

Rockets are unguided, I think you mixed up with missiles.

@Cypc Yea, thank you. In german "rocket" and "missile" is the same, so I mixed them up.

They both belong in the category of countermeasures, but let's say that they... target different audience. Chaff is used to spoof radar guided (active or semi active) missiles. Flare is used to spoof heat seeking (passive) missiles.
Chaff pods contain several small metallic parts of similar size and shape and their aim is to create false returns to the radar beaming the targeted aircraft. The sized and shape depends on the radar wavelength they try to spoof but I am unaware of the exact relationship.
Flare on the other hand targets heat seeking missiles. As user3528438 mentioned in their comment, they are "fireworks" that aim to create a brighter thermal image and drive the missile away of the aircraft's thermal trail.
The tricky part for the pilots (and perhaps the modern warplane designers) is to distinguish between the type of the homing missile, so that they use the right countermeasure for each threat without wasting consumables. That's probably the reason you've heard them as chaff/flare like there is no difference.

There are two ways for an anti-air missile to "see" its target:

Radar signature : the missile is fitted with a radar receiver, so when the launching plane illuminates his target with his radar, the missile get the signature and can go to the target. (Some more advanced missiles even have their own little radar emitter and receptor for the last part of their guidance.)
Heat signature : the missile is fitted with a heat seeker, and will follow the eat source he was assigned by the launching plane before firing.

Chaffs are designed to defeat the first category, flares the second :

Chaffs are small pieces of material that will reflect radar waves in different directions. Their goal is to disrupt attacker's radar so he can not guide his missile or will guide it on the chaffs, not the defending plane.
They do not produce any smoke and are really difficult to see visually.
Flares are small pieces of material that will produce a lot of heat, trying to blind / confuse the enemy eat seeking missile, making him think one of the flare is in fact the planes engine.

In both cases they are employed to try to divert a missile from his target.

Flares are normally pyrotechnic devices designed to create a large IR signature to capture IR targeting on missiles.
There are two common types of chaff.  The most common is metal based and is reflective, designed to create a field of reflections and capture the radar receiver.  They are not necessarily foolproof.  For example, their velocity drops to the ambient wind velocity within a few seconds, were as an aircraft will continue to depart at a flight velocity.  Also, metastatic radar and other techniques may see around / through them.
There is also IR chaff (also a pyrotechnic measure) which is designed to create a field of temperature, reducing the signal to noise of the targeted aircraft (or other target) and decreasing the capture and hold on that target.  The effectiveness of IR chaff is similar to RF chaff as reported by several sources.

Could you include a source on the IR chaff? A cursory search doesn't seem to bring it up.

@AEhere sure.  Just had a student do a paper on IR chaff. There are many DTIC papers, but an open reference is: EW 102, David L Adamy, (2004) page 105.  Keep in mind that chaff is different from flares, in that flares are larger devices and chaff is small.  This means that flares generally are sensed as point sources, and chaff is rather a distributed region.


text:
What does steering angle mean?
I'm reading the UAVSAR data format and in File Naming Convention section is said that if we take a typical file name:
Dthvly_34501_08038_006_080731_L090HH_XX_01.slc

as the name that follows
Dthvly_34501_08038_006_080731_L  (090)  HH_XX_01.slc

The three digits that are in parentheses, is the steering angle.
And for the above file name, we have:

Dthvly is the site name, 345 degrees is the heading of UAVSAR in
  flight, with a counter of 01, the flight was the thirty-eighth flight
  by UAVSAR in 2008, this data take was the sixth data take during the
  flight, the data was acquired on July 31, 2008 (UTC), the frequency
  band was L-band, pointing at perpendicular to the flight heading (90
  degrees counterclockwise), this file contains the HH data, this is the
  first interation of processing, cross talk calibration has not been
  applied, and the data type is SLC.

What is steering angle?
Please explain very simply because I'm not very familiar with aviation concepts. I just want to have a sense and intuition about of the aircraft steering angle.

The only thing that the internet seems to reference with that is the angle of the nose gear from being centered ( "centered" meaning that the plane would be going straight if it was on the ground).  Does that sound like it fits what you're looking at?

The steering angle, in these files, refers to radar beam steering. In this case the radar is rotated 90 degrees ccw with respect to the flight heading, effectively looking into the 255 degrees direction. Voted to close as off-topic / too specific

@JayCarr At first I thought it is the central angle of the curved path of the plane? but three things make me dubious. 1- Plane is not always on a curved path, so we don't always need to report steering angle.      2- In order to uniquely specify the curved path, central angle is not enough. We need the radius of the curve, too. Then why don't we report that radius in file's name?      3-  the bold center in the quoted part pointing at perpendicular to the flight heading (90 degrees counterclockwise) also makes me dubious

@DeltaLima what does ccw mean? Also I thing it's not an off-topic question. Because at the first look, we think steering angle definition is the one said by Jay Carr. I also searched for that https://www.google.com/?gws_rd=ssl#q=aircraft+steering+angle and I thought it should be related to navigation and aviation

ok I understood. ccw means counter clock-wise

CCW = counterclockwise.

Steering angle, according to the text you bolded:

pointing at perpendicular to the flight heading (90 degrees counterclockwise)

means the steering angle 090 is the angle, relative to the flight heading counterclockwise, that the data sample was taken.
If the flight heading was 345 degrees, 90 degrees counter clockwise (CCW) is 255 degrees.  This steering angle has no aviation context and is just a relative offset from the aircraft heading for data acquisition (which in this case sounds like a radar sample).


text:
What are the slides that ATCs use for tracking departures and arrivals?
I've seen ATCs use little slides with flight numbers for tracking arrivals and departures - is there a term for them and are they still used today with modern ATC terminals?

Yes they are called flight progress strips or simply strips. They are still in use, though they tend to be replaced more and more by the electronic strip or e-strip.
They are also used by en-route controllers (not only terminal as you mentioned). From my experience from Athens ACC, PALLAS supports e-strips, but there is also a printer that prints them in some intervals (I don't remember what triggers the print). Note that some time ago, during the procedural control era, those were manually completed by the ATCOs. I guess they are still manually completed in TMAs and ACCs that use procedural control as primary method and lack RADAR service.

I'm guessing they are also still used as a redundancy measure in the however unlikely case the triple-redundant set of mains power, diesel generators and batteries all fail simultaneously. (Although how to keep in radio contact in that case is somewhat of a challenge. Handhelds?)

I am not aware about the redundancies used in ATC, but in case RADAR fails, I'm pretty sure they fall-back to procedural, part of which is handwritten strips.

@JörgWMittag, the ATC facilities do usually have hand-held radios as a communication tool of last resort, though not in sufficient number and power to keep any sort of regular operation; they'd probably just use them to hand off everyone to some other facility in case all power failed. And note that land lines don't need power, so they could give that other facility as much information as preserved on the printed strips.


text:
What is the energy demand of a secondary surveillance radar?
I'm writing a report to see if it's feasible to power a secondary surveillance radar with wind energy. I'm having trouble with sizing the turbine but I can't seem to find an energy demand for a SSR anywhere. any help is appreciated.

What kind of SSR do you need to power? What range, what update rate /revolutions per minute. Mode A/C or Mode S. How many aircraft in range?

This one with a range of 300 km has a peak power of 2 kW. That likely means you need 3 or 4 kW to feed it. Technical characteristics. You surely need to have displays, processing power and a backup power source.

@mins, that figure is probably excluding the motor for turning the antenna assembly. But in total 4 kW should be about right.

@mins I am not sure whether it is the peak transmission power or it is the average power consumption during peak capacity operation of the whole radar chain, including scheduler, interrogator, receiver, extractor and output generator. The beam itself may have a high peak power, but the duty cycle is quite low because most of the time the receiver is connected to the antenna. When the radar is transmitting, it will draw power from its capacitors, those are recharged while the radar is listening to the reply.

What you propose is possible.  TCAS is essentially a secondary surveillance radar, and is a piece of avionics which doesn't break the bank power wise. In a moderate traffic environment, I have seen 3 to 5 amps at 24VDC.  I am sure it is higher in a dense environment.  The interrogation power requirement doesn't go up but processing the returns may take more power.
5 amps at 24VDC is a modest power requirement for a mid-sized wind energy system, therefore at first blush, what you propose is quite possible.

Uh... a typical SSR has quite different requirements from TCAS. Yes, they use similar concepts, even the same frequencies and data formats but the range and azimuth requirements are in an entirely different league

TCAS range is 4.5 NM/14 NM, in relative silence of air, not compatible with ATC use.

I was hoping to get the energy demand in kWh.

@darragh That's nonsensical, like asking how fast a car is, measured in feet. Besides, P=U*I, so that's 120W for TCAS (although I also doubt whether that is a realistic number for a ground station).

@mins, TCAS I is advertised to be good to 40 mile radius.

@darraghmcsweeney, I used TCAS as an example of SSR which is relatively low power and could be used in a wind energy configuration, even a small one.  If you wanted a full blown SSR, that was not clear to me, because that could include processors, display stations, or whatever you desired as support equipment.  So I scaled to something that would meet your basic requirement, and be within a small to mid-sized wind energy system.

A full blown SSR such as http://www.easat.com/download/brochure/MSSRLR.pdf will require in excess of 20 kW/hr and would require a larger wind energy system with substantial storage capability.  Is it possible? Yes, but you might need a small wind farm and storage facility.

@Sanchises my apologies, i've background is electrical engineering. so I'm only familiarising myself with a it's jargon and units of measurements. but the turbine I've found that produces 25VDC and 5-6 amps only generates 400 watts, I may be wrong but it seems quite low?

@darragh Again, power is current times voltage. 25V*6A=150 watts. I'm not sure where you're getting 400 watts from. And, for a small wind turbine, a few hundred watts seems very reasonable - that's about the power of a large computer or a small vacuum cleaner.

"TCAS I is advertised to be good to 40 mile radius": It can detect a signal at 40 NM, sometimes. That's not the same than being reliable (90%) at 14 NM and being guaranteed at 4.5 NM.

@darraghmcsweeney If you can't effortlessly convert among SI units like W and kW and figure out how kWH relates to kW ... don't quit your day job :)  You can get kWH from kW if you know how many hours (H) you plan to run this thing.


text:
Can a Greek EASA Part 66 License be converted to a German EASA Part 66 License?
I want to convert my Greece Part 66 license to a German Part 66 license. What procedure do I have to follow?

You have to send the request to the Greek Authority.
They will contact the German one, and the German Auth. will probably contact you to fill a Form 19.
(details depend of the Auth. procedures)

This is helpful, Do you have access to any Greek or German reference material that would help back up this answer? If so, [edit] in links (with appropriate quotes in the body of the answer) to make it a great answer.


text:
Does it make sense to use a canard in combination with a conventional aft elevator control surface?
I am designing a UAV and have settled on a canard design.  However, I’m curious whether it would be helpful to have a typical horizontal stabilizer behind the wing as well as a canard wing in front of the main wing to increase lift towards the front of the plane and for better stablity.  Is this a bad idea? I’m looking to carry cargo ranging from 0-1000g, and initially fly for around 30 minutes. It is also using a special VTOL system I’ve designed.

Hey Awesome, could you maybe add some info on the mission profile of your UAV?

Are you carrying weights/cargo so the center of gravity would shift during the mission?

I made some info changes!

If you optimize for extreme efficiency you should avoid generating any lift, positive or negative, except the main wing, because only the main wing has the highest lift to drag ratio. The reason canard has the advantage of lower drag under some conditions is because at super sonic speed, center of lift shifts backwards so much that the leverage of aft elevator is too short which calls for a very large negative lift on the elevator. Your plane won't fly supersonic so it won't take advantage of that.

Oh! Thank you.  The canards are necessary because I need to be able to put things, most notably the vtol system, in front of the wing.  Canards will allow the cg to go out much further.  But I Definitly see your point.

@user3528438 sorry didn’t tag you on the above comment.

Actually, for most tasks it would be most helpful to add the horizontal tail and to remove the canard. There have been only a few canard designs and even fewer three-wing designs in the past. Off-hand I remember just three:

Voisin-Farman biplane in the Musée d'l Air in Paris (picture source)
Gabriel Voisin was the founder of the first commercial aircraft factory and designed a biplane with forward elevator and aft stabilizer in 1907 for Léon Delagrange and Henry Farman. He had chosen a similar layout for his very first glider design in 1905 already, most likely because the question where the elevator goes on an airplane was a matter of hot disputes at those times.

The second one is of course the excellent Piaggio P.180 Avanti (picture source), where the highly loaded canard allows to move the wing behind the pressurized cabin and the lightly loaded elevator provides ample control authority at all flap settings and center of gravity locations.
The third one is the Sukhoi-30 MKI, which adds small, closely-coupled canard wings to the conventional layout of basic the Su-27 / MiG-29 design. Thinking of experimental Russian designs, I could also mention the MiG Ye-8, a MiG-21 with a free-flying canard surface (picture source):

If you don't expect to have a wide center of gravity range in your UAV, use fewer wings. One big one for the lift and a second one for stability and control should be all you need.

There are many variants of the SU-27/30/35 family which have both canards and tail planes. The SU-30MKI is an excellent example.

Interesting! The reason I need the canards is I need to balance out the vtol rotor system and payload both of which are forward of the wing. The vtol config won’t work if it’s behind the wing for various reasons, so I need the canards to help allow me to move the cg forward.

@Moo: Yes, good addition - I was probably too focused on civilian planes.

@PeterKämpf sorry I didn’t tag you on my comment ^^

@TristanSemmelhack: No problem, if you answer the author of a question in a comment, he/she gets an automatic notification, even without tagging.


text:
If you turned base early, cutting off other traffic, what is the safest way to rejoin downwind?
Joined the left traffic pattern at a controlled field downwind.  Controller informed me I was number three for landing. Saw traffic on final, turned base, reported to tower "following cessna on final". Controller comes back a minute later and realizes I cut off a plane on final and I was now number two (my mistake here.  I realize now, I think, I should have not maneuvered at all unless I was 100% sure I could see planes 1 and 2 on final). Controller tells me to rejoin the downwind.  At this point, I was still on the base, so I turned right to rejoin the downwind and the plane behind me that was on final passes too close below me while I am executing a turn from base back to the downwind.  Didn't seem safe.  In fact, as soon as the controller told me to rejoin the downwind, that didn't seem safe.  I am not sure what I should have done.  I could have A) had more situation awareness and turned left to get back to the downwind  B) called for a go around (on a base?), moved to the upwind leg (not departure) and rejoined the pattern. C) the controller should have told the plane on final that was behind me to get out of the patter by going around to the upwind leg.
I realize I caused this issue by maneuvering to base following the wrong plane.  Like most aircraft incidents, it is usually a combination of factors. I caused the first, did I cause the second?  Should I have called for a go around. What should the controller have done?
In the future, I can fix my issue. But what do you do if you are cutting off for whatever reason a plane on final, while you are on base. What is the safe way to get out of the situation.  Ideas?  Thanks

Control or no control, If I'm told that I'm number three, I won't make any turn before having 1&2 in sight. Otherwise, I'll prolong downwind (or base), leave the traffic area, and make a very wide turn before entering again downwind.

Yeah, I think that pretty much sums up my initial mistake. Now assume you made it already OR the controller made a mistake and you need to leave the base leg, how do you safely do it assuming there is an aircraft on final to your right?  I guess it isn;t that hard, and you just have to turn left and tell the controller

How about climb back to pattern altitude, turn final offset in the direction of traffic by a few hundred feet, fly to the departure end (keeping traffic on final in sight), and then turn cross wind, and then turn back to downwind?

Interesting, but you're not the first to encounter this situation. I understand from what you say that you were going to wedge in between the no 1 and no 2 traffic already established on final.
Given the circumstances and not time to think about this, the preferred option would be to turn left to rejoin downwind. Assuming no other traffic in the pattern. Then you are turning towards the other traffic. A left turn would have given you a full 270 degree and time to regroup
Should there have been other traffic on the left base then they would be positioned further downwind from your position. You may become a conflict for them then by turning right.  Equally there may have been traffic joining downwind like you did in which case a left turn could become a conflict to them.
This is just assumption. I'm just pointing out the need for full on situational awareness particularly in the circuit. Need to know where all traffic is relative to you.
Finally, I would say it would have been more reassuring for the controller to specify “turn left/right now to rejoin downwind”. If you had made it to final then a missed approach would be the way out and continue rwy heading until advised.

Could you offer a more definite answer there instead of the stream-of-consciousness thoughts on the original post?

"the preferred option would be to turn left to rejoin downwind." -- do you mean "turn left to rejoin the upwind?"

@Wayne, from a left base one could turn 90º left to join upwind or turn 270º left to re-join the left downwind. Or even fly through final and turn 90º right to join the right downwind, if the controller asked.

I think that calling for a missed approach for a go around would be the appropriate action. This would necessitate an immediate climb over the runway. Statistically, this is the safest place in the pattern. I would preferably side step slightly right of the runway (assuming that I am in the left seat). So that I can keep an eye on any arriving or departing aircraft below me while staying approximately directly above the runway.
If the controller clears you for left or right closed traffic, then you could rejoin the traffic pattern upon reaching the DER at the appropriate Traffic Pattern Altitude. If ATC requests an immediate turn back to downwind, continue the climb while in the turn, in the same direction as the traffic pattern turns. Consider it under the same argument as all turns in the traffic should be in the same direction of the traffic pattern except the actual initial entry from outside of the traffic pattern.
Try not to turn to rejoin the downwind (and definitely not the base) until approximately midfield. Give way to all other traffic established in the pattern. As per AIM 4-3-5, “ Except when requested by the controller or in emergency situations, a 360 degree turn should never be executed in the traffic pattern or when receiving radar service without first advising the controller.”
If you do not get clearance to rejoin traffic, leave the traffic area. Then, rejoin the traffic pattern using the proper radio calls and 45 to downwind procedures. Either way, take your cues directly from the controller.
In my opinion, this would be the safest option while giving you time to re-establish yourself for a stabilized approach.


text:
How can I test a COM VHF antenna?
I have an older VAL 760 TSO COM radio. Twice now the radio has blown an internal radio fuse on transmit. VAL has tested and certified the radio as "Good", but advice that the cable or antenna could be faulty. How does one test that the antenna or cable is adequate? Can one use an ohm meter to check for resistance or continuity? Any other advice is appreciated. I have a newer VHF antenna. It may be a CI-101, although not positive.

Just a suggestion: If the cable/antenna was wrong, the fuse would probably have no time to blow, that would be the power amplifier transistors. In addition if they are protected against impedance mismatch, nothing should happen except a bad reception and bad transmission. So, as the unit has been checked, I would now check the other connections, specially any existing DC output (to power external devices or switch), as this could be a short-circuit between +Vcc and the ground.

Your radio shop may be able to test the SWR of the antenna working with the COM radio.  That would be my starting point.  However, sometimes problems like these are intermittent and difficult to isolate.
You can test the antenna with an ohm meter but that will not measure the impedance at transmit frequencies.  An SWR meter will.
Unfortunately, unless your other hobby is ham radio, you may not have the equipment on hand to check out transmitter operation.  But your radio shop will.
They will also have a dummy load for testing the transmitter.
I have to say that I am surprised that the unit blew a fuse.  Most aviation radios I have experience with (I am not an avionics tech only a ham) have protection against shorts or opens on the output of the transmitter, which usually shut down the power of the transmitter, for example when a high reflected signal comes back. So blowing fuses is normally extremely rare.


text:
What are IFR departure categories?
I'm looking at the takeoff mins and DPs for Reno/Stead (RTS.)  It lists takeoff mins for Cat A and B, Cat C and D NA:

TAKEOFF MINIMUMS: CAT A,B only, CAT C,D NA. Rwys 8,14,  1300-2 or std.
  with a min. climb of 400' per  NM to 6500.  Rwy 26,  1900-2 or std.
  with a min. climb  of 410' per NM to 7200.  Rwy 32,  2300-2 or std.
  with a  min. climb of 420' per NM to 7200.
  (Source)

What are the departure categories?  I can't find any mention of them in the instrument flying handbook.

Could be this category.

@mins Actually, the smaller aircraft CAN use the DP as long as they have either the ceiling/vis and/or the climb performance; the "CAT C,D NA" means that the larger aircraft can NOT use the DP under any circumstances.

The categories are actually approach categories that are also used for departures. From the AIM, 5−4−7. Instrument Approach Procedures

Aircraft approach category means a grouping of aircraft based on a
  speed of VREF, if specified, or if VREF is not specified, 1.3 VSO at
  the maximum certified landing weight. VREF, VSO, and the maximum
  certified landing weight are those values as established for the
  aircraft by the certification authority of the country of registry. A
  pilot must use the minima corresponding to the category determined
  during certification or higher.

Category A: Speed less than 91 knots.
Category B: Speed 91 knots or more but less than 121 knots.
Category C: Speed 121 knots or more but less than 141 knots.
Category D: Speed 141 knots or more but less than 166 knots.
Category E: Speed 166 knots or more.

These categories are used to determine visibility and ceiling minimums for an approach and determine the protected area for circling approaches. As you can see in the departure minimums you quoted, they are also used for departures.